Soil, as the main Component of natural ecosystems, provides significant contribution to sustainable use of land resources. These days, soil erosion and desertification lead to many problems for agricultural production and cause threat to food security in global scale due to population growth. Arid to semiarid regions with long dry seasons are very susceptible to runoff production, soil erosion and subsequently to soil degradation as compared to humid areas. This investigation was conducted to evaluate the efficacy of biochar on the reduction of soil erodibility under simulation rainfall experiment. Biochar is a carbon enriched porous material with low density which is produced by heating organic matter under low-oxygen conditions. In the current study, four levels (0, 0.5, 1 and 2 percent by weight) were selected to evaluate the effects of sewage sludge and its biochar on runoff and sediment yield in a silty clay loam and a sandy clay loam soil. Experiments were designed in three replicates in plots with 1 m 2 area and 8 percent gradient. Amendments were incorporated to upper parts of plots and incubated for 3 months. After one and three months of incubation some soil chemical and physical properties (including organic matter, saturated hydraulic conductivity, shear strength, aggregate stability and bulk density), as well runoff and sediment production under rainfall simulator (with an intensity of 60 mm h -1 ) were measured. The results of study showed that the application of both amendments increased soil organic matter, soil shear strength and also the aggregate stability. Furthermore, specific sediment yield, sediment concentration and bulk density reduced in both soils studied. Runoff production decreased in silty clay loam soil with increasing the rate of amendments application, while runoff increased in sandy clay loam soil. Negative and significant correlation (P 0.01) was found between soil organic matter and runoff and sediment yield. Moreover, shear strength showed significant relationship with runoff. The highest runoff and sediment yield were obtained in control treatment, while all the treated soils showed lower values compared to the control sample. The highest impact on runoff and sediment yield was observed in 2 % of sewage sludge and biochar application. Overall, longer period of time (3 months as compared to 1 month) led to higher impact of applied amendments and resulted in the reduction of soil erodibility in both soils. Additionally, sewage sludge and biochar application could reduce bulk density and increase aggregate stability and soil shear strength in both soils with time. Key words: Water erosion, biochar, sewage sludge, runoff, rainfall simulator, specific sediment yield, saturated hydraulic conductivity.